DETERMINATION OF THE HEAT REQUIREMENTS DURING THE ECODORMANCY FOR THE CHERRY (PRUNUS AVIUM) IN BULGARIA

Abstract

In temperate climates, fruit crop yields are primarily determined by environmental conditions, especially during dormancy and in the early stages of their phenological development. Climate anomalies, with both warmer spring temperatures and greater temperature fluctuation, have altered phenology, leading to a greater risk of spring frost damage to orchards. The sweet cherry (Prunus avium), like other fruit species in the temperate climate, needs to accumulate a cultivar-specific quantity of chilly units during the endodormancy, and heat units during ecodormancy for breaking of dormancy and flowering properly in spring. The knowledge of chilly and heat requirements is important in the selection of the appropriate cultivars for the produces in a particular area. This study aims to estimate growing degree hours (GDH) requirements up to flowering for 12 cherry cultivars grown in the basic regions of industrial cherry production in Bulgaria. Phenological and hourly temperature observations for nine years (2002-2010) were used to perform this study. The GDH were calculated as the sum of temperatures above 5�C accumulated from the breaking of dormancy to the flowering. The heat requirements (HR) for flowering ranged between 1908-3868 GDH. The results indicate that the flowering time of cherry in the studied regions is influenced by GDH. Identification of cultivars with higher HR and later flowering is important for cherry production, especially in regions with frequent late spring frosts occurrence.